Developer composition containing solvent removable organic pigment and method of flaw detection

ABSTRACT

THE USE, IN THE COLORED LIQUID PENETRANT METHOD FOR DETECTING SURFACE DISCONTINUITIES IN A WORKPIECE, OF A DEVELOPER COMPOSITION COMPRISING A DISPERSIN IN A LIQUID VEHICLE OF FINELY DIVIDED DISCRETE PARTICLES OF AN ORGANIC PIGMENT THAT IS INSOLUBLE IN SAID LIQUID VEHICLE BUT THAT IS SOLUBLE IN CHLORINATED AND FLUORINATED HYDROCARBON SOLVENTS. AFTER APPLICATION OF THE DEVELOPER COMPOSITION TO THE PENETRANT-TREATED SURFACE AND THE DISSIPATION OF THE LIQUID VEHICLE, THE REMAINING LAYER OF PIGMENT PARTICLES FORMS, WITH ANY RESIDUAL COLORED PENEETRANT COLOR, INDICATIONS THAT ARE VISIBLE TO THE OPERATOR UNDER APPROPRIATE RADIATION TO INDICATE THE LOCATION AND EXTENT OF ANY SURFACE DISCONTINUITIES. THEREAFTER, THE RESIDUAL DEVELOPED COLORED INDICATIONS ARE COMPLETELY REMOVED BY DISSOLUTION IN A CHLORINATED OR FLUORINATED HYDROCARBON SOLVENT, AS BY THE USE OF A SOLVENT DEGREASER.

United States Patent Office 3,542,654 Patented Feb. 15, 1972 US. Cl. 252-408 7 Claims ABSTRACT OF THE DISCLOSURE The use, in the colored liquid penetrant method for detecting surface discontinuities in a workpiece, of a developer composition comprising a dispersion in a liquid vehicle of finely divided discrete particles of an organic pigment that is insoluble in said liquid vehicle but that is soluble in chlorinated and fiuorinated hydrocarbon solvents. After application of the developer composition to the penetrant-treated surface and the dissipation of the liquid vehicle, the remaining layer of pigment particles forms, with any residual colored penetrant color, indications that are visible to the operator under appropriate radiation to indicate the location and extent of any surface discontinuities. Thereafter, the residual developed colored indications are completely removed by dissolution in a chlorinated or fiuorinated hydrocarbon solvent, as by the use of a solvent degreaser.

CROSS-REFERENCES TO RELATED APPLICATIONS This is a continuation-in-part of my co-pending parent application for patent Ser. No. 619,000, filed Feb. 27, 1967, now abandoned, and constitutes an improvement over the invention disclosed and claimed in US. Patent No. 2,707,236, dated Apr. 26, 1955, exclusively licensed to the owner of said parent application and of this continuation-in-part thereof.

SUMMARY OF THE INVENTION This invention relates to a developer composition adapted for use in the colored liquid penetrant method of non-destructive testing for the detection of surface discontinuities, flaws, cracks and the like. The developer composition is applied to the surface of the workpiece undergoing test after the application of a colored liquid penetrant and after the removal of any excess of penetrant from the surface without, however, removing penetrant entrapped in any surface flaws.

The developer composition of my. invention is intended to be used in place of previously known wet developers that comprise dispersions of finely divided inorganic pigments or solids such as talc and the like, in a solvent-type liquid vehicle such as a water-soluble alcohol or a volatile hydrocarbon or chlorinated hydrocarbon liquid in which the pigment is, of course, insoluble. Such wet developers have been used in the penetrant method for the nondestructive testing of surfaces to detect discontinuities therein. The penetrants commonly used are those that are of an oily nature, including petroleum hydrocarbons and other water-immiscible oils and solvents, used either as such or containing an emulsifier, or surfactant, that perm its the liquid penetrant to be removed by water washing. These types of liquid penetrants can be used in conjunction with the developer composition of my present invention. While it is preferred that the penetrant be one that is colored by dissolution therein of a visible dye, rather than a fluorescent dye, fluorescent dyes can be used, in

which case the developed color indication will be observed under black light, i.e. filtered ultraviolet light.

The improvement in the developer composition of my invention is believed to reside in the use, as the pigment, of an organic solid that is insoluble in the liquid used for suspending the pigment particles but is soluble in solvents such as are suitable for use in a solvent degreaser system, namely, in chlorinated or fiuorinated hydrocarbon solvents, whereby after the application of my developer composition and the removal of the liquid vehicle thereof by evaporation, drying or the like, the finely divided particles of the organic pigment remaining on the surface can be removed in a vapor degreaser system, or by dissolving the pigment otf of the surface by the application thereto of the foregoing solvents.

Prior to such removal, the developer composition acts to develop a color indication by drawing out of any surface discontinuities the coloredliquid penetrant or such residue thereof as may be entrapped therein. Such drawing out of the entrapped penetrant is the result of the conjoint solvent action of the liquid vehicle of the developer composition before dissipation of said liquid vehicle, and the capillary action of the residual layer, after such dissipation, of closely adjoining discrete solid particles of the organic pigment upon the colored liquid penetrant to spread the same and thereby enhance the visibility of the resulting color indication.

Where hitherto known developers have been used, it has been necessary to remove the residual developer layers from the surface undergoing test by an often tedious process of washing with water and scrubbing. In view of the solvent action of chlorinated and fiuorinated hydrocarbons toward the dye of the penetrant and also the organic pigment of the developer, the discrete organic pigment particles remaining as a color indication on the surface tested can be simply and expeditiously removed in a vapor degreaser system or by the application of hot chlorinated or fiuorinated hydrocarbon solvents. In a few seconds the object or part undergoing test is complete free from any pigment particles as a result of such solvent action.

It is therefore an important object of this invention to provide a developer composition comprising an organic pigment that is insoluble in the liquid vehicle of the penetrant but that is soluble in chlorinated or fiuorinated hydrocarbon solvents and a method for its use, wherein the pigment coating remaining after development of the color indication and drying of the developer composition can he simply and expeditiously removed by subjecting the surface undergoing test to the solvent action of a chlorinated or fiuorinated hydrocarbon, as for instance, in a solvent degreaser system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

My improved developer composition comprises, in general, a liquid suspending vehicle containing a solid organic pigment dispersed (or dispersible) therein in a finely divided state. The liquid vehicle for suspending the developer pigment is preferably a volatile organic liquid which is a solvent for the dye used in the colored liquid penetrant to aid in drawing out colored penetrant residues entrapped in any surface discontinuities, but the suspending vehicle must, of course, be a non-solvent for the suspended developer pigment. Suitable liquids for suspending the developer pigment are volatile, highly polar solvents, such as the lower molecular weight, C C water-soluble aliphatic monohydric alcohols, preferably unsubstituted, such as isopropanol (which has a boiling point of about 80 C.). At temperatures below about 100 F. the developer is relatively insoluble in any of the suspending liquids.

The solid organic pigment selected should, of course, be insoluble in the liquid used for dispersing the pigment, and while meltable, it should have a high enough melting point to be solid at the highest normal operating temperatures to which the developer composition is subjected in use as a developer, normally about 80-85 F, yet have a low enough melting point to melt at whatever temperature, up to about 250 F. (the boiling point of perchloroethylene), at which a vapor degreaser solvent is used for dissolving the pigment 01f the tested surfaces. Solvents such as perchlorethylene, trichloroethylene, or trichlorotrifluoroethane are among those in which the pigment is soluble at their boiling points. Preferably, nonflammable solvents are employed.

Examples of suitable solid organic pigments are: diphenyl phthalate, which is a White powder, crystallizing at about 69 C., soluble in ketones and esters, and in chlorinated hydrocarbons, but insoluble or only slightly soluble in lower boiling point alcohols such as ethanol at room temperature; octadecane, which is available as needle-like crystals having a melting point of 28 C., a boiling point of 3057 C., soluble in ether and acetone, and slightly soluble in lower boiling alcohols at room temperature; methyl beta naphthyl ether, having a melting a point of 72 C., and slightly soluble in ethanol; and acenaphthene, available as needle-like crystals, having a melting point of 96 C., a boiling point of 278 C., and slightly soluble in ethanol at room temperature. All of these organic pigments are sufilciently soluble in the aforementioned chlorinated and fiuorinated hydrocarbon solvents to be removable in vapor degreasers employing such solvents.

In order to increase the ease of dispersing the solid organic pigment and maintain it suspended in the selected liquid vehicle it is preferable to use a surfactant compatiible With the liquid vehicle to function as a dispersant for the pigment particles. A great many surfactants can be used for this purpose, but, by way of example, I have found that any of the following surfactants are most suitable as an anionic surfactant, a sodium salt of a alkylaryl polyether sulfonate, available in liquid form as a 30% concentrate, or a sodium salt of an alkylaryl polyether sulfate, available in paste form as a 20% concentrate; as a cationic surfactant, stearyl dimethyl benzyl ammonium chloride, available as a paste of 25% concentration, or as an 82% active dispersion in isopropanol; and as a nonionic surfactant, a nonyl phenyl polyethylene glycol ether; available as a 100% active liquid.

My developer composition consists essentially, then, of the organic pigment, the surfactant-dispersant therefor, and the liquid vehicle for suspending the pigment. The ranges by Weight can be: solids content from to with the organic pigment content preferably constituting about 10% by weight of the total composition; the surfactant-dispersant preferably about 1.25% active ingredients by weight of the composition; and the balance, the liquid vehicle. The percentage of dispersant should be sufficient to give the desired degree of dispersibility to the developer composition so that the finely divided pigment particles can be redispersed if they have settled out on standing. However, the amount of surfactant can be varied between 0.9 and 2.5% by weight and give good results, with 1.25% optimum.

If the organic pigment, as for instance, diphenyl phthalate, is not available in sufficiently finely divided form, as purchased from the supplier, it is preferably ground or milled to an average particle size of about microns, although somewhat finer or coarser size particles can be used quite satisfactorily. In general, the finer the particle size, the greater the capillary action of the pigment particles toward the colored liquid penetrant, or penetrant residue, in or about the surface discontinuity, and consequently, the greater the visibility of the color indication upon development.

The developer composition of my invention is particularly suitable for use in a dyed liquid penetrant method for detecting surface discontinuities in which the penetrant has dissolved therein a dye that is also soluble in the liquid vehicle of my developer composition. In that event, upon application of my developer composition to the surface undergoing test after the removal of the excess of penetrant from the surface, the liquid vehicle of my developer composition serves to dissolve the entrapped dye and/or dyed penetrant or penetrant residue and draw the same out to the surface. Then, upon evaporation of the liquid vehicle of the developer composition, the dry, finely divided organic pigment particles that remain on the surface in discrete by closely adjacent solid form serve by capillary attraction to draw the resulting dye solution up into or onto the particles and thereby form a color indication of enhanced visibility to the unaided eye. Where as is preferable, the dye used in the penetrant is a visible dye, the indication is examined under visible or white light. Fluorescent dyes can, however, be used satisfactorily under the same conditions as to liquid suspending vehicles, pigments, etc., and the resulting fluorescent color indications examined under black light.

After the observation of the color indication, or color indications, has been by the operator, the remaining developer coating is readily removable by placing the object undergoing test in a vapor degreaser and there subjecting the remaining pigment coating to the action of the degreaser solvent to dissolvent away the pigment. Any of the usual chlorinated or fluorinated hydrocarbon solvents that are or can be employed in a vapor degreaser system will readily dissolve any of the foregoing named organic pigments. The chlorinated hydrocarbons include perchloroethylene and trichloroethylene, and also methylene chloride, ethylene dichloride, tetrachlorethylene and admixtures of two or more thereof, as well as other blends commongly used in solvent degreasers. The useful fiuorinated hydrocarbon solvents are usually mixed chlorineand fluorine-containing compounds that are very volatile but are liquid at temperatures below about F. Trichlorotrifiuoroethane has a boiling point of about 117.6 F.

If the temperature at which the organic developer pigment is removed is a temperautre above the melting point of the pigment, the molten pigment dissolves more rapidly into the solvent used in the solvent degreaser system than when in solid form.

The following will serve to illustrate a preferred manner of application of my developer, with reference to the use of a colored liquid penetrant such as any of those described in the so-called post-emulsification patent to De Forest et al. No. 2,806,959.

EXAMPLE A colored penetrant such as that of Formula No. 4 is used comprising:

Percent by volume VM & P Naphtha 75 Partially hydrogenated terphenyl 25 and a visible dye, No. 322 Metford Oil Red dye in the amount of 3 grams per 100 ml.

After the application of said penetrant to the surface undergoing treatment, a liquid emulsifying agent is applied over the penetrant treated surface to render the penetrant removable with water. Any excess of emulsifier and penetrant is then washed off the surface with water without removing unemulsified penetrant from surface discontinuities in which the penetrant has become entrapped. This is all described in the aforementioned patent.

Thereafter, in accordance with the present invention, my developer composition is applied by immersion of the workpiece into a bath of said composition, or by spraying or flooding the composition over the surface of the workpiece. After allowing the applied developer composition to dry, well-defined color indications appear, if a visible red dye is used in the penetrant, wherever surface discontinuities of sufiicient dimensions have entrapped the colored penetrant.

After inspection, the residual developer composition left on the surface is removed by placing the workpiece in a vapor degreaser employing a chlorinated or fluorinated hydrocarbon solvent that is a solvent at its boiling point for the organic pigment used as the active developer in my developer composition.

I claim:

1. A developer composition for use in the colored liquid penetrant method of detecting surface discontinuities by developing color indications from colored penetrant residues entrapped in such discontinuities, said composition consisting essentially of a liquid suspension of finely divided particles of an organic pigment that is relaitvely insoluble in the suspending liquid at temperatures below about 100 F., but readily soluble in hot liquid chlorinated hydrocarbon solvents, said organic pigment being selected from the group consisting of diphenyl phthalate, octadecane, methyl beta naphthyl ether and acenaphthene wherein said suspending liquid is a relatively volatile C C water-soluble aliphatic monohydric alcohol.

2. A developer composition as defined wherein said alcohol is isopropanol.

3. A developer composition as defined by claim 1, wherein said alcohol is an unsubstitued alcohol.

4. In a method of penetrant inspection for detecting surface discontinuities, the steps comprising applying to a surface a colored liquid penetrant, removing from said surface excess penetrant but leaving penetrant residues entrapped in any surface discontinuities, applying to said penetrant-treated surface and drying thereon a suspension of finely divided pigment particles in a liquid vehicle by claim 1,

adapted to develop color indications by the conjoint dissolving and capillary action of said liquid vehicle and of said pigment particles, respectively, toward any entrapped penetrant.

said pigment being an organic compound selected from the group consisting of diphenyl phthalate, octadecane, methyl beta naphthyl ether and acenaphthene that is soluble in hot chlorinated hydrocarbon solvents, but is insoluble in said liquid vehicle, and removing said pigment from said surface by a solvent selected from the group consisting of chlorinated and fluorinated hydrocarbon solvents.

5. A method as defined my claim 4, wherein said liquid vehicle is a relatively volatile C C water-soluble aliphatic monohydric alcohol.

6. A method as defined by claim 5, wherein said alcohol is isopropanol.

7. A method as defined by claim 6, wherein said pigment is an organic compound selected from the group consisting of diphenyl phthalate, octadecane, methyl beta naphthyl ether and acenaphthene.

References Cited UNITED STATES PATENTS 4/1955 De Forest 250-71 9/1957 De Forest et al 73--104 US. Cl. X.R.

23-230 L; 73-l04; 25071 R 

